Our research group in the Endocrine Unit at the Massachusetts General Hospital has been funded for its basic research efforts as a Program Project for the last decade. Our research during this period has involved extensive efforts to understand basic details of the hormonal regulation of calcium and phosphate metabolism and to apply the insights gained and the methods developed to improve diagnosis and management of clinical disorders of calcium and bone metabolism. We believe the progress achieved by our group during this period has been substantial. When coupled with the great progess made in other laboratories in the U.S. and abroad, it is clear that the large body of accumulated information pertinent to hormonal regulation of calcium metabolism provides a base from which extended further effort can lead to a much better defined and quantitative picture of calcium and phosphate homeostasis and a clearer understanding of the physiological significance of these metabolic and homeostatic processes.